Process of treating zinc ores



Dec. 5, 1 933. c s 1,937,633

PROCESS OF TREATING ZINC ORES Filed Sept. 23, 1931 2 Sheets-Sheet l cenfitgrams Zm 21 Q) Q g per cc. Solution,

Percerm H SQ,

INVENTOR WJZKW .100 9O 80 70 6O 50 4O 5O Z0 Perceni Acid,

Dec. 5, 1933.

N. C. CHRISTENSEN PROCESS OF TREATING ZINC ORES Filed Sept, 23. 1931 ZrzS Ore or o lyiw Zinc *Meiallio Zahc/ INVENTOR.

Ff Z.

ublimed Zinc Oxide Patented Dec. 5, 1933 H mamas-f p PROCESS OF TREATING ZINC omits Y .Niels C. w(dhristenscn,. saltLake City, Utah I I I Application Septemberf23 1931 Q 7 f Serial No. 564.6% A 8 claims. (01; 23-135) This invention relates to the treatment of zincores. It relates-primarily tcthehydrometallurggical treatment. of raw zinc sulphide ores so as to recover the: zine and sulphur therefrom Without I roasting. Inthe treatment of the sulphide ores in the process a smaller proportion ofv oxidized oreisalso treated. for the recovery of zinc. therefrom; The invention relates to the treatment of the sulphide ores with sulphuric acid by the" nwmethods similar to those described in my 00- pending patent applications 523,575 and 523,576, filed March.1-8,. 1931, which describe the applications of the process to the recovery of thezinc in metallic formby electrolysis. It is the'object 1. oflthisinven-tion to recover thezinc as other produets and by slightly diiierentmethods than those described in said applications.

Asdescribed in above mentioned pending paten-t applications, the first and essential stepof m the process consists in. treating the ore with hot relatively concentrated sulphuric acid in, such manner' as to decompose the-Z113 and .form solid zinc sulphate and H23. As noted in above said. applications and as. more fully described in. my U. S. Patent 14 34 084, hot sulphuric acid'of a concentration of approximately or higher will attack. forming ZnSQeand drive on the sul-' ph-ur as H28. If sufficient HzSOq is used: the

extraction of the zinc maybe secured. However, as-notedinabove said, patent and applications, a relatively very large volume of acid-must be used to secure complete} solution. of. the zinc by this method due to thelimitedsolubility of; ZnSO. in gmthe acid. If a=relatively small amount of acid is used, the reaction. between the acid and the ZnS stops as-the saturation point of the acid'in the ZDSOIL is; approacheddue to the formation of an insoluble superficial coating of 221504 upon the A ZnSparticles which protects the sulphide against further; action by the acid. As noted in thecopending, patent. applications mentioned above, I have foundthat this superficial coating. may eas1v ily beremoved by a gentle grinding or attrition,

and thus allow the reaction between the hot. acid and. theZnS particles to proceed until the 2118 is all converted into solid zinc sulphate. By thus grindingthe zinc sulphide ore 'witlethe hot acid a. complete conversion of theZnS to solid- ZnSO; occurs. Thismethod makes it possible to sulphatev all-the. zinc in the ore and drive oil the sulphur asHzS by the use of a relatively very small proportion of hot acid,- ascompared. with that required theprocess of Patent #1,43'4 ,08., .The very large: volume of acid required in thelatter offer no difficulties in practical application.. Follow-ingthe sulphating operationthe excess 63 Zn'SQi dissolves in the excess acid and a complete a process is a serious handicapincommercial-om; A oration, whereaswith theprocess of thisinventionr. the volume of acid required is so-sma-ll astoof hot acid is separated fromthe ore. residue and solid zincsulphate by filtration. The filter cake containing the ore residue; zinc sulphate and some residualfacid isthen mixed with sufficient hot ater to form ahot concentrated. acid, zinc 6i;

sulphate solution. Ths acid in: this solutiomis neutralized with oxidized zinc ore and any iron. and manganese precipitated from solution. dur ing this treatment by addition: of suitableoxi dizing agent. This neutralizing and purifying 701?. step may be carried out either by separating the hot acid zinc sulphate solution from the insoluble ore residueby filtration and washing" and thereafter treating the solution; with-the oxidized ore and oxidizing. agent, or by'mi-xing the oxidized ore' 1 and oxidizing agentw-ith; the mixture of ore residue and. acid zinc sulphate solution. The second method saves one complete mixingnfiltering-i and'washing operation and is therefore preferred unless it. is desired to keep); the leached 8&5

ore residues separate. The hot concentrated'zinmf sulphate solution thus formed is separatedwfrom the-leached ore residue and treated with zinc dust. to precipitate Cd, Cn,;Ag, Pb, from thesolu tion'. The pure hot concentrated zinc sulphates solution thussecuredis utilized for making,- zincr sulphide, basic zinc carbonate zinc oxide,-. cr metall-ic zinc as briefly described-inv the-following:2- for the direct manufacture of ZnS- the? precipitated from: this solution: aspureizn-s by 9 treatment with has or Na(S-H) made fromtthe- H25 generated in the sulphating treatment, or to: make'a calciumbase lithopone-(mixture: of'ZnS'? and CaSOt) by precipitation. withCa(SI*lE)'-2.-solu+= tioix madefrom. theHzS generated in: me n-4%; phating treatment. The zinc sulphide product-f thus madeis filtered, washed, dried; calciued 500C quenched; andi'groundwto' form alwhite zinc 'sulphide pigment. To make the: basiczinccarbonate, the hot"v concentrate solution is; mixed. with CaClsolution to form a I zinc chloride solution and precipitate GaSOA -aS indicatedi'in the-foll'owingc'liemical equation:

. ZnSO4+CaC1z=CaSO4+ZhCl2 p 105? The. hot. zinc. chloride solution thus formed is; separated from the. CaSOt precipitate byfiltra: tion, and. washing and thezinc is precipitated. therefrom as a basic zinc carbonate by boiling llfizinc sulphate I cated by the following chemical equation:

This ZnS is filtered, washed, dried, calcined, and quenched and ground to make a white zinc sulphide pigment. The basic zinc carbonate may also be calcined to convert it to zinc oxide. The zinc oxide thus formed may be used as a pigment,

. or may be reduced with carbon or natural gas in a retort to secure metallic zinc, may be treated upon a Wetheril grate to'make sublimed zinc oxide, or vmay be treated with I-IzS from the sulphating operation to make ZnS according to the following chemical equation-z The ZnS thus formed being filtered, dried, cal- I cined, quenched, and ground to form the white ZnS pigment. The zinc may also be recovered from the basiczinc carbonate or the zinc oxide by utilizing either of them to neutralize the acid formed inan electrolytic zinc circuit and thus =recover the zinc therefrom by electrolysis.

The methods of carrying outthe invention, as briefly outlined above, in its different applicacations, is' illustrated in the accompanying flow sheets. The accompanying curves also illustrate the limiting conditions for efficient operation at importantpoints in the process.-

Figure I consists of two curves A and B showing the solubility of zinc sulphate respectively in hot and incold acids of different concentrations.

' Figure II shows a flow sheet of the process indicating the important steps and apparatus in the process.

As noted above, the essential and most im-' portant step in the process consists in grinding" thefinely divided .ore'with an excess of hot sul phuric acid of a concentration preferably between 60% and 65% until the zinc'is converted to ZnSO4, the sulphur being. driven ofi as H28) This operation is preferably carried out in an acid-proof 'silex or porcelain'lined pebble millf called the sulphator (1), containing small flint pebbles'or porcelain marbles as the grinding medium. The mill should preferably be jacketed and insulated to maintain the temperature and pre- Though there is some reaction jvent loss "of heat.

between the acid and zincsulphide at lower temperatures the reaction proceeds most rapidly at temperatures near the boiling point of the acid 1 and it is preferable to keep the acid as near this' :Itemperature as possible-during the grinding. From 10 to 30 minutes grinding is sufficient to sulphateisubstantially'all the "zinc in ores that are amenable totreatment by the process. In

' order to save the H28 and keep it free from con- 'tamination with air, the ore and hot acid are fed into the mill at the feed end through a gas tight gland and the mixture of excess acid and sulphated ore and the H28 gas are discharged through a gas tight gland into a discharge box at the discharge endfifrom which thesulphated the solution with finely divided CaCOa as indipulp and excess acid flows, preferably through a shallow inverted siphon, to the filter (2) and from I ore preferably as hot 98% H2804. If the larger volumes of circulating acid are used this acid maybe mixed with the incoming circulating acid,

but if the smaller volume of circulating acid is used, the amount of 98% acid to be consumed in sulphating is preferably added progressively during the sulphating operation in order toavoid the use of acid of sufficient'concentration to react with the H23 and increasing the acid. consumption. j

The consumed acidincludesthat used in sulphating the ZnS, etc., in the sulphide ore and also the acid neutralized by the oxidized ore.

The mixLure of sulphated ore and excess acid of oxidized ore used in the process the filter cake is given a flash wash with Water to remove as much more of the acid as possible without dis-f from 65% to 50% does'not greatly increase the solubility of the ZDSO4. The excess circulating acid and washings from the acid-proof filter (2) are passed through the heater and concentrator (3) where the wash Water is evaporated and the acid is heated for reuse and returned to the sulphator as shown. The I-IzS goes to the absorber (4) Where. it is absorbed in an emulsion I of Ca(OH) 2 in water to form a Ca(SI-I) 2 solution or may go to an acid plant or sulphur recovery plant.

The filter (2) must be acid proof and must be 160 from the sulphator (1) passes to the filter (2) asmuch as possible of the acid is removed by filtration and if it is desired to cut down theamount As will be noted by reference to the supplied with an acid proof filter medium such as filtros, alundum, 01' acid proof metal filter cloth. The sulphated pulp filters very readily and a roiating annular Vacuum filter of the sandfilter type may be'used for this purpose, or a pressure filter such as the Burt may be used.

:If the excess of acid used inthe sulphating operation is kept as low asfpossible, it-may not be necessary or possible to remove any excess of hot acid by filtration and this second step of the process may thus be avoided-andthe'sulphated ore be sent directly to the Washing or neutralizing operation, as described below. For practically complete recovery of the zinc, however,.I have found that with most ores it is preferable or'necessary to use such an excess of acid in the su1-;

phating operation that the greater part of this excess must be separated from the ore before neutralizing in order to avoid the use of too large a proportion of-oxidized ore.

The concentrator and heater (3) may be of any standard type of apparatus but the preferred type slightly dipping into the acid which is thus thrown from the drum as a spray through which hot combustion gases are passed to evaporate the.

Water and heat the acid.- The HzS absorber (4) newness any Cu, CdQ-Ag', or Pb, etc.-, in the solution and the consists preferably of a similar device, though ny other suitable standard apparatus may be The zinc sulphate in the filter-cake from the filter (2) may be recovered either of two'ways as indicated respectively as AA and B- -B in the flow sheet. In the first method, A to A, the acid filter cake is mixed withsunieient hot water in the agitator (5) to dissolve the zinc sulphate and acid to form a hot acidconcentrated zinc sulphate solution. To this-mixture enough oxidized zinc ore (or zinc-lead ore) isadded to neutralize the acid and dissolve the zinc out of the oxidized ore, and enough of an oxidizing agent such as lead peroxide, zinc peroxide, or chloride oi'lime or other suitable oxidizer to precipitate the iron and manganese out of the zinc solution. This neutralizing and cleaning operation is carried out at a temperature between 69 and so C. (or higher) so as to secure a zino'sulphate solution of high concentration. The hot neutral zinc sulphate solution thus formed is washed out of the mixed leached residue of sulphideand oxidized ore by filtration and Washing. This operation preferably carried out by means of a dewaterer or filter (6) followed by a washing operation in a counter-current'washer (7) and final filter (8), as shown in the flow sheet,'the wash solutions from the counter-current washer (7) and filter (8') being added to the agitator(5)' to dissolve the zinc sulphate out of the sulphated ore. from the sulphator (I).

In the second method, B to B, the acid filter cake from the filter (2) is mixed with suilicient hot water in the agitator (15) to dissolve the zinc sulphate and form a hot acid concentrated zinc sulphate solution. This acid solution is separated from the residue of leached lixi'viated' sulphide ore in the dewaterer (16) and the re sidual zinc sulphate. solution is separated from the residue of ore in the counter-current washer (1 7). and filter (18), the wash solutions from (1'1)! and (18) being added to the agitator (1 5) to dissolve the ZnSOr as shown in'the flow sheet- The hot acid zinc sulphate solutionvis mixed with sufi'icient oxidized zinc (or zinc-lead) ore: to neutralizezthe acid and dissolve the zinc the oxidized ore, inthe agitator (25) enough oxidizing agent being added near the end or this treatment to insure complete precipitation of any iron and manganese inthe solution. Thehot concentrated zinc sulphate solution thus-formed is separated from the leached residue of oxid-i'zed ore in the dewaterer (26) and the residue of ore separated from the: residual solution in the counter curren-t washer (27) and filter 28),

the wash solutions being returned to the agi-tator" ('15,) for dissolving 211804- from the Sui-pirated sulphide ore.

The mixed residue of sulphide and oxidized ore from AA and the separate ore. residues from B-B may be treated by the brine leaching process toxr'ecover any lead (or lead and silver) therein and the residue may be treatedby flot'a-- tion to recover the pyrite therefrom, or the resi dues may be discharged to waste if they contain no recoverable values. Any silver in solution may be precipitated from the 211804 solution by the addition of sufi'ic'i'ent ZnClz after neutralizing, or may be recovered from the ZnSO4 solution by means oi metallic zinc as mentioned below. I

The hot concentrated neutral zinc sulphate solution obtained from A --A-or- BB is treated with zinc dust in the agitator (31) to precipitate precipitatedmetals and excess Zn dust are filtered out of the solution in the filter (32).

The pure hot concentrated zinc sulphate solu- I tion obtained by the foregoing processes may be treated in a variety oi'ways to prepare it for market vor to' make' marketable zinc products therefrom as described in the following:

' The zine sulphate solution may be marketed as such' or may be evaporated to secure hydrous or anhydrous ZnSO4 for market. The solution may also be used to make lithopone by the stand ard methods. It-may also be used to make pigment zinc sulphide or calcium base lithopone as described in the following: The -Ca(SH)2 made in theabsorber (4) may be used to precipitatethe ZnSO4 solution and form *a mixed precipitate of 09.801 and ZnS as indicated by the following m al equationz A- small excess of Ca(SH)z is preferably used in this precipitation. The mixed precipitate preferably containing some excess Ca(SH)z is filtered" out of the solution and dried, calcined,'quenched and ground, washed and dried to make a calcium. base lithopone consisting of anhydrous CaSOi and zns. The excess H2S from the precipitation is returned to the absorber (4) to make more concentrated Ca(SII) 2 solution. be precipitated from the ZnSO4 solution by means The zin'c may also of NaSH made from the Ca(Sl-I)z from the ab sorber (4) as indicated in the following chemical equation:

. ziiso;+2Nasn=zns+n2s+N so4 A small excess of NaSI-I'or some Ca(SH)2' should also preferably be present in solution at the end of this precipitation. The Nazs'Oi is filtered "out of the precipitate and is used to make the NaI-IS (sodium sulphydrate) sorber (4) according to Ca (SH) 2+Na SO =CaSO +2NaSH solution from theab- The excess HzS' from the Z'nS'preci-pitation'is re-' during the filtering operation is dried, calcined, quenched, and ground washed and dried to make a zinc sulphide pigment 'The excess 'Ca(SH)e retained in the Z-nS precipitate during the calcination improves the light resistant qualities ofthe pigment.

The zinc sulphate may betreated with a Ca'Clz solution. in the precipitator (9) to precipitate CaSO4 and form a purezinc chloride solution as indicatedbel'owz the following equation? amount of lit The ZnClz. solution being separated out ofthis solution in the dewaterer (l0) and then seperated from the residual ZnChsolution by :washing in the counter-current washer (37) and filter (8), the wash solutions being mixed with the ZIlClz solution from the dewat'erer (10). (If it' is desiredto market the ZnCl solution'as such, a rela tively concentrated CaClZ solution is securedfrom 1 an external source, but if thefZ'nClz solution is to be used for preparation of other'zinc products as shown on the flow sheet, the'CaClz solution is obtai'ned' describedbelow.)- The hot diluteZnCIi solution'thus obtained is heated to boiling and a" chemical equivalent of finely divided (ground or precipitated) 02.003 to ZnClz in solution, is added and this mixture boiled until the zinc is substantially completely precipitated as a basic zinc carbonate. The precipitation requires from 30 minutes (or less) to an hour depending upon the. fineness of the CaCOz. To secure substantially complete precipitation, the solution should preferably not carrymuch above 2 zinc, as the completeness of precipitation decreases with increase in concentration of the ZnClZ solution as shown in Fig. I. The precipitated zinc product obtained'as above described is not pure basic zinc carbonate but contains some unconsumed CaCOs and some G1 which may be removed as described below. The basic zinc carbonate precipitate is separated from the hot relatively dilute CaClz solution in the dewaterer (12) and the CaClz so-- lution is sent to the CaSOr precipitator (9) as shown upon the flow sheet. The residual CaClz is separated from the basic zinc carbonate precipitate in the counter-current washer (l3) and the washed precipitate. is ground with hot-water in the treater (consisting of a pebble mill or other suitable grinder)' (l4),to complete-the reaction between the CaCOa and ZnClz contained in the precipitate. The treated precipitate is then separated from the solutionby filtration in the filter (48). The wash water from the filter (48) and the wash water used in the treater (14) are both used in the counter current washing operation and then mixed with the CaClz solution and :passed through the evaporator and heater (60) (preferably of the rotor cylinder spray type previously described) to evaporate the excess water before being returned to the precipitator (9).

' The treatment of the basic zinc carbonate precipitate by grinding and washing with hot water may be repeated depending upon the degree of purity desired. If either the CaCOa or Cl are'in excess during this treatment sufficient CaCO; or

'ZnClz may be added to bring them into equi molecular proportions.

The basic zinc carbonate secured as outlined above may be dried and marketed as such. It may also be used to neutralize the acid in a rapidly circulated electrolytic zinc circuit so as to maintain a highly concentrated and substantially neutral ZHSO4 solution in the circuit and make electrolytic zinc therefrom with a considerable increase in economy over present electrolytic practice. It may also be calcined in the calciner (49) as indicated in the flow sheet to make zinc in metallic form as described above for the basic oxide. This product may be marketed as such as a zinc oxide pigment or may be used in an electrolytic zinc circuit for-the recovery of the zinc zinc carbonate. If the 2110 is marketed as a pigment it should preferably be calcined at a high temperature since this treatment. gives a pigment of higher covering power than the oxide formed at lower temperatures, whereas if the oxide is to be dissolved it should preferably be calcined at a lower temperature (SOT-400 C.) .to secure'a more readily soluble product.

The zinc oxide .made by calcining the basic carbonate may also be treated upon a Wetheril grate to make sublimed zinc oxide or may be treated in a'retort plant to recover the zinc in metallic form. The zinc madefrom this product 'by retorting is equal in purity to the best grades of electrolytic zinc.

The basic zinc carbonate and the zinc oxide may both be used to make a high grade pigment zinc sulphide by treatingthem in emulsion in water with 1-128 from the sulphator (1). This operation is preferably carried out by passing the H28 from the sulphator (1) into a spray formed of the water emulsion of the basic zinc carbonate or oxide in the sulphidizer (50) until the products are completely sulphidized, as indicated below;

The sulphidizer is preferably of the rotating cylinder spray type, enclosed in a housing as previously described. The ZnS from the sulphidizer is filtered and washed (if necessary) upon the filter (51) and is then dried and calcined in the calciner (52) at a temperature above 500 C. (preferably between 625 and 675 C.) and is then quenched and thereafter finely groundto make the finished zinc sulphide pigment. The product made in this way is a white pigment of high tinting'strength and covering power and is very resistant to light. I s

From the foregoing brief description it will be apparent that the invention makes possible the treatment of raw zinc sulphideores in such a.

form solid zinc sulphate and drive off the sulphur as HZS and thereafter filtering excess acid away from the mixture of solid zinc sulphate and ore residue using said acid in the treatment of more ore, and mixing said solid zinc sulphate and ore residue with sufiicient waterto dissolve said solid zinc sulphate and form an acid zinc sulphate solution and addingsufficient oxidized zinc ore to said mixture to neutralize the acid in said solution and sufiicient oxidizing agent to precipitate theiron and manganese therefrom, and separating said neutral zinc sulphate solution from the mixed ore residues and precipitated impurities and treating said neutral solution with metallic zinc to precipitate therefrom metals below zinc in the electromotive series and separating the pure neutral zinc sulphate solution from said precipitated metals and excess of metallic zinc, and making calcium sulphydrate solutionby treating an emulsion of calcium hydroxide in water with said H25 from the first step, and precipitating above last said zinc sulphate solution with said calcium sulphydrate solution to form a mixture of zinc sulphide and calcium sulphate and filtering and calcining, quenching and grinding said mixed precipitates to form a mixture of calcium sulphate and zinc sulphide suitable for use as a paint pigment.

2. The process of treating zinc sulphide ores centration as to decompose the zinc. sulphide and drive off the sulphur as H28 and thereafter filtering excess acid away from. the mixture of solid zinc sulphate and ore residue and using said acid in the treatmentof more ore, and mixing said solid zinc sulphate and ore residue with sufficient water to dissolve said zinc sulphate and form an acidzinc sulphate solution, and adding sufficient oxidized ore to said mixture to neutralize theacid in said solution and suflicient oxidiz- Mil messa agent ;to,;precipitate-the iron and manganese -therefrom, and separating said neutral zinc-sulphate solution from the mixed ore -;residues 7 and -precipitated impurities and treating v said solution Iwith -metallic zinc to precipitate :metals .Joelow .zinc the 'electromotive series therefrom, and separating-the pureneutral zinc sulphate solution iromsaid precipitated metals and excess oin eitallic .-zinc, and making a calcium sulphydrate solution by treating an emulsion of calcium hydroxide in water with -H2Sfl'0l1l the above de- --scribed treatment of zinc sulphide ores with sulphuric acid, andtreatingsaidcalcium sulphysdrate, solution with a sodium sulphate solution,

:made as described below, to precipitate calcium sulphate-and make a-sodium sulphydrate solution,

andprecipitating thelzinc-from said lpureneutral zinc sulphate solution Withsaid last mentioned sodium 'sulphydrate solution to make zinc "sul- .p ide and a sodiumsulphate solution, and sepa- -rating said szinc sulphide from said sodiuin sul- -,;phate solution and using last said solution to ;make :more sodium sulphydrate solution as de ,scribed above, and calcining, quenching and phate and :Viorin an-acid; zinc sulphate solution, and separating said acidv zinc sulphate solution afromsaid ore residue, and treating said acid zinc sulphatesolution with oxidized zinc ore to heutralize the acid therein and an oxidizing agent toprecipitatethe iron and manganese therefrom, and separating, the neutral zinc sulphate solution thus formed from the residue of oxidized ore,

(andtreating said neutral zinc sulphate solution with metallic zinc to precipitate therefro n'imetal s below zinc in the electromotive series and separating said precipitated metals and excessof metallic zinc from said purified zinc sulphate solution, and making. calcium sulphydrate; soluas l-above =descrihed and precipitating said purified zinc sulphate solution with said calcium sulphydrate solution to form'a mixture of zinc sulphide and calcium sulphate, and filtering and calcining, quenching and grinding said mixed precipitates to form a mixtureof calcium sul-" j phate and zinc sulphide suitable for use as a paint pigment. V

4, The process of treating'zinc sulphide ores andconcentrates which consists in grinding said ores and the like with such an excess of hot relatively concentrated sulphuric acid of such con-.-

centration as to decompose. the zinc sulphide and form solid zinc sulphate and drive ,oif the sulphur as H28, andvthereafter filtering excess acid away from the mixture of zinc sulphate and ore: residue and using said acid in the-treatment'of more ore, and mixing sufilcient water with said solid zinc sulphate and ore residue to dissolve said zinc sulphate and form an acid zinc sulphate solution and separating said acid zinc sulphate w from said ore residue, and treating said acid zinc ,to, precipitate therefrom sulphate solution with oxidized ore to-neutralize he a i h r a dka oxidizing a en t ore- ,cipitate-the iron and manganese therefrom; and separating the neutral zinc sulphate from the resid -o x di ed r a s r ti s a aid n u-. tral solution ith metallic zinc to precipitate therefrom metals lower than zinc in the {electr cmotive series; and makin a calcium sulphydrate solution by treating an emulsion of calcium hy- 1f0xld in water-withI-ES made fifOlIlgZlllCjSjllv phide ore as above described, and treatingsaid calcium 'sulphydrate' solution with a sodium sulphate solution, ,in ade as described helomto -;pre- .-cipitatecalcium sulphate andmake'a sodiumsul; rh e o ie i andjp c it t s t e, z n tram last above said purezinc sulphate solution with last said sodium sulphydrate, solution-to make zinc sulphide A and a sodium {sulphate solution, and separatingsaid zinc sulphide from said v sodium sulphatef solution and using last said lution to makemore sodium sulphydrate solu N1 'asdescribed above, and calcining, quenching and grinding said zinc sulphide to make a :zinc sullphide suitableforuseasapaintpigment.'

5. The process of treating .'zinc-. sulphideores and concentrates which consists in grinding said ores and the like ith-such an excess of hot relatively ;conc e'ntrat;ed sulphuric z;acid of such t a onya ydewmnqs the zi s lphide and :form-solidzinc sulphate anddriveofi the acid awayirom the mixture of solid Zinc suli 0 sulphur as H28 and thereafter filtering excess}- phate and oreresidue-using said l acidin the re im o m e. e, land/ x said soli zinc sulphateand ore residue with sufiicient vvater,

agent to'precipitate the iron-. ,and-manganese he m --and ra i s d n a -zin i phate solution from the mixed ore residuesand treating said neutral solution with metalliczinc Y metalsbelow zinc in the elect iomotive series and separating the pureneu- ,tra} zinc sulphate solution from said precipitated metals'and excess of metallic" zinc, and making calciumsulphydratesolution-hy'treating an emulsionof calcium hydroxide in ater with above said 1-128, and precipitating iabpve. last said zinc sulphate solution with said calcium s ulp hydrate vtion bytreating anemulsion of calcium hydroxide in Water with P128, made from zinc sulphide ore solution toiorin a mixture of zinc sulphide and calcium sulphate, andl using the excess I -12S generatedlin last said precipitationfto snake-more I calcium su'lphydrat'e as described-for use in pre-' cipitating more zinc sulphide as described, and filtering andcalcim'ng, quenching and'gr'inding said mixed precipitates to form a mixture of cal i'cium sulphate and zinc sulphide suitable for use as a paint pigment.v

6. The process of treating zinc sulphide ores w and concentrates'which consists in grinding said ores andthe like ith such an excess of hot relatively concentrated sulphuric acid of such' and adding suficient oxidized ore to said mix-: I I

ture to neutralize the acid in said solution and sufiicient oxidizing agent to; precipitate the; iron:

using 1 110 to dissolvesaidsolidzinc sulphate and form-an and drive off the sulphur as H28 and thereafter and manganese therefrom, andseparating said neutral zinc sulphate solution from the mixed ore residues and treating said solution with metallic zinc to precipitate metals below zincin the 'electromotive series therefrom, and separating the pure neutral zinc sulphate solution from said precipitated metals and excess of metallic zinc,

" using theexcess HzS'generated in last said precipitation to make more calcium sulphydr'ate'as described for use in the process as described, and separating said zinc sulphide from said sodium sulphate solution and using last said solution to make more sodium sulphydrate solution as described above, and calcining, quenching and grinding said zinc sulphide to make a zinc sulphide suitable for use as a paint pigment.

7. The process of treating zinc sulphideores and concentrates which consists in grinding said ores with such an excess of hot relatively concentrated sulphuric acid of such concentration as to decompose the zinc sulphide and form solid zinc sulphate and drive off the sulphur as H23 and thereafter filtering excess acid away from the mixture of zinc sulphate and ore residue and using said acid inthe treatment of more ore,

and mixing with said solid zinc sulphate and ore residue sufficient water to dissolve said zinc "sulphate and form an acid zinc sulphate solution, and separating said acid zinc sulphate solution from said ore residue, and treating said acid 'zincjsulphate solution with oxidized zinc ore to neutralize the acid therein and an oxidizing agent to precipitate the iron and manganese therefrom, and separating the neutral zinc sulphate solution thus formed from the residue of oxidized ore, and treating last said solution'with metallic zinc to precipitatetherefrommetals below zinc in the electromotive series and separating said precipitated metals and excess of 'metallic zinc from said purified zinc sulphate solution, and making calcium sulphydrate solu-T: tion by treating an emulsion of calcium hydnoxide' in water with l-IzS, made from'zinc sulphide ore as above described and precipitating last said of zinc sulphide and calcium sulphate,and using the excess HZS generated in last said precipitation to make more calcium sulphydrate as described for use in precipitating more zinc-sul phide as described, and filtering and calcining,

quenching and grinding said mixed precipitates to form a mixture of calcium sulphate and zinc sulphide suitable for use as a paint pigment.

purified zinc sulphate solution with last said calcium sulphydrate solution to form a mixture 8; The process of treating zinc sulphide ores and concentrates which'c'onsistsin grinding said ores and the like with such an excess of hot relatively concentrated sulphuricacid of such concentration as to decompose the zinc sulphide and form solid zinc sulphate and drive off the sulphur as H25, and thereafter filtering excess acid' away from the mixture of zinc sulphate and ore residue and 'using'said acid in the treatment of more ore, and mixing sufficient water with said solid zinc sulphate and ore residue to I dissolve said zinc sulphate and form an acid zinc sulphate solution and separating said acid zinc sulphate from said ore residue, and treating said acid zinc sulphate solution with oxidized ore to neutralize the acid therein and anoxidizing agent to precipitate the iron and manganese therefrom, and separating the neutral zinc sulphate from the residue of oxidized ore, and treating last said neutral solution with metallic zinc to'precipitate therefrom metalslower than zinc in the electromotive series, and making a calcium sulphydrate solution by treating an emulsion of calcium hydroxide in water with l-IzS madefrom zincsulphide oreas above described, and treat- 7 ing said'calcium sulphydrate solution with a sodium sulphate solution, made as described below, "to precipitate calcium sulphate sodium' sulphydrate solution, and precipitating the zinc from last above said pure zinc sulphate solution with last said'sodiun' sulphydrate solution to make zinc sulphide and a sodium" sul-' phate solution, and using the excess Has generated in last said precipitation to make more calcium sulphydrate as described for main the process as described, and separating said zinc sulphidefrom said sodium sulphate solution and using last said solution to make more sodium sulphydrate solution as described above, and cal-- cining, quenching and grinding said zinc sulphide. to make a zinc sulphide suitable for use as a paint pi ment.

7 NIELS C. CHRISTENSEN;

andmake 'a Certificate of Correction Patent No. 1,937,638.

e printed specification of the above numbered patent requiring correction as follows he; and line 91, f0 N0 read with these corrections therein that th case the Patent Office.

SIgned and sealed this 20th day of Fe (Seal) F. M. HOPKINS, Acting Commissioner qf Patents. 

